Process for the production of a shaped part from pieces of sheet metal of different thicknesses

ABSTRACT

A shaped member of welded pieces of sheet metal of different thickness, more particularly having a metallic anti-corrosion protection, for example of zinc, on at least one side, wherein the pieces of sheet metal are joined to one another by a laser-beam-butt-welding process and shaped as a unit.

This is a division of application Ser. No. 135,194, filed Dec. 18, 1987,now U.S. Pat. No. 4,827,100.

The invention relates to a process for producing shaped parts shaped bypressing or deep drawing from welded sheet metal pieces of differentthicknesses, more particularly pieces having a metallic anti-corrosionprotection, for example of zinc, on at least one side.

Shaped sheet metal parts are as a rule subjected to differential loadingin individual zones. Examples of shaped parts subjected to differentialloading in this way are the parts of a motor vehicle, more particularlythe bottom plate. If such structural components are dimensioned for themaximum loading, not only is material wasted, but more particularly theshaped parts are unnecessarily heavy. These disadvantages can beobviated if the shaped parts are of different dimensions in theindividual zones, in accordance with their loading.

DISCUSSION OF PRIOR ART

For example, it is known to make up the shaped parts from a number ofindividually shaped pieces of sheet metal of different thicknesses. Theindividual pieces overlap one another at their edges and are weldedtogether by resistance welding or fusion welding.

With a shaped parts of the kind specified the advantages of savingmaterial and lower weight are offset by the disadvantages of veryexpensive manufacture. A large number of individual tools are requiredfor the shaping of the individual pieces of sheet metal. The doublethickness of material, not really required for stability, in the zonewhere the edges overlap must be accepted to allow the interconnectionwithout elaborate adjusting work of the pieces of sheet metal, which mayalso be shaped in their edge zones. In the case of surface-protectedpieces of sheet metal, the cut edges are left open and the surfaceprotection is destroyed by the welded joint, more particularly in thecase of fusion welding. Lastly, the use of fusion welding leads torelatively large zones whose structure and strength differ from those ofthe remaining zones uninfluenced by the welding. Since in the spotwelding of overlapping edge zones the zones between the welding placesare open, as a rule as additional seal is necessary.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a process for the productionof shaped parts which enables such parts to be produced, whilemaintaining a construction which saves material and weight, not only ina simpler manner, but also with the least possible loss of quality incomparision with the base material. Another objective of the inventionis to provide corresponding shaped parts.

In the process according to the invention, flat pieces of sheet metal ofdifferent thicknesses are butt welded with a laser beam without addingfiller material and then shaped as a unit by pressing or deep drawing.

In the case of a shaped parts shaped by the pressing or deep drawing ofwelded pieces of sheet metal of different thicknesses having a metallicanti-corrosion protection, for example of zinc, on at least one side,the solution to the problem according to the invention is that thepieces of sheet metal are connected to one another by alaser-beam-butt-welding process and shaped as a unit.

In comparision with the prior art process, with the process according tothe invention the costs of production are lower for several reasons.Since during welding the pieces of sheet metal have not yet been shaped,they can be welded to one another without relatively elaboratepositioning work. Shaping is performed in one step on the welded unitand no longer separately for each piece of sheet metal. Due to the knownprocess of butt welding by laser beam (German Patent Application P No.35 023 68 A1) the welding zone can be small and precisely adjusted, sothat the welded joint alters the material structure and strength of onlynegligibly small zones of the overall unit in comparision with theremaining zones. Since during laser beam welding, coatings like zinc inthe welding zone evaporate and do not get into the melt, moreover noessential change takes place in the structure of the material of thejoint, at any rate the material remains shapeable even in the zone ofthe joint. Due to the low expansion of the joint being welded withoutusing filler material, the material adjacent the welding joint is"sacrificed" during the shaping operation if the material of the jointon its own cannot share in the deformation. Lastly, due to the lowexpansion of the laser-beam-welded joint, the effect of remoteprotection is achieved, i.e., even in the zone of the joint, which isitself not protected against corrosion, for example, by a layer of zinc,it shares in the protection afforded by the adjacent anti-corrosionlayer. To enable joints as narrow as possible to be laser beam weldedwithout the addition of a filler, the corrugations of the abutting cutedges in the plane of the sheet metal in longitudinal direction shouldnot be greater than 0.04 mm and the spot of the laser beam not greaterthan 0.2 mm.

According to a preferred embodiment of the invention, the pieces ofsheet metal should be welded from one side, the surface of the pieces ofsheet metal lying on that side being offset in relation to one another.In that case the result is a transition between the surfaces of the twopieces of sheet metal in the form of a groove.

The positioning of the laser beam spot and the direction of the beaminfluences the proportion of the material to be melted in both pieces ofsheet metal and therefore also the formation of the welded joint. Inthis case it has been found to be advantageous if the laser beam is soguided that the thicker piece of sheet metal contains the largerproportion of the melting zone.

Also advantageously welding is performed with the laser beam directed atan angle to the surface of the pieces of sheet metal, one component ofthe beam direction being directed towards the exposed cut edge of theprojecting piece of sheet metal.

To prevent undefined energy irradiation into the material due toreflection of the laser beam, the beam should be kept away from thetransitional zone between the exposed cut edge and the surface of thethicker piece of sheet metal.

A root-side drop-through or a root-side suckback of the joint on theroot side of the welding location can be obviated in a very simplemanenr if a gas cushion, more particularly of inert gas, acts on therear side of the pieces of sheet metal in the welding joint zone atleast during the molten liquid phase.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION Brief Description of theDrawing

The invention will now be described in greater detail with reference tothe drawings

FIGS. 1 to 4 are side views of welded joint zones of pieces of sheetmetal of different thicknesses; and

FIG. 5 is a perspective view of pieces of metal of different thicknesseswelded together; and FIG. 5A is a sectional view shown along line A-B ofFIG. 5.

Detailed Description of the Embodiment of the Invention

Referring to the embodiment illustrated in FIG. 1, surfaces 1, 2 ofpieces of sheet metal welded together lie in one plane on the weldingside. In contrast, in the embodiment illustrated in FIG. 2 the surfaces5, 6 of the two pieces of sheet metal 7, 8 lying on the welding side areoffset in relation to one another. While in the embodiment illustratedin FIG. 1 welding is performed with a laser beam 9 directedperpendiculary to the surfaces 1, 2, in the embodiment illustrated inFIG. 2 the laser beam 10 is directed at an inclination to the surfaces5, 6, one component of the beam direction being directed towards theexposed cut edge 11 of the thicker piece 7 of sheet metal, although thetop corner 12 is not acted upon by the laser beam 10. A comparison ofthe shape and extent of the two welds 13, 14 indicates that the weld 14(embodiment illustrated in FIG. 2) is more favorable, since there isless risk that the toe cracks may occur more particularly in the rootzone of the weld.

To prevent a root-side drop-through or root-side suckback at theunderside of the joint 14, the joint 14 can be borne at that place on agas cushion. To this end in the embodiment illustrated in FIG. 2 acooling element 18 having a duct 21 is placed on the undersides 15, 16of the two pieces 7, 8 of sheet metal. The duct 21 is in the zone of thejoint 14 and is filled with inert gas at excess pressure. The inert gasprevents a root-side drop-through on the underside 22 of the joint 14.Of course, it is possible for the joint to be borne on the rear side ofthe welding side with a suitably adapted cooling element in theembodiment illustrated in FIG. 1 also.

The embodiments illustrated in FIGS. 3 and 4 differ from thoseillustrated in FIGS. 1 and 2 by the feature that the surfaces 23-26,29-32 of the two pieces 27, 28, 33, 34 of sheet metal are offset inrelation to one another; another difference in the embodimentillustrated in FIG. 4 is that the corners at the cut edge of the thickerpiece 33 of sheet metal are so chamfered that the height of the end facesubstantially corresponds to the thickness of the thinner piece 34 ofsheet metal. A similar adaption of thickness may be convenient if thereare considerable differences in thickness as between the two pieces ofsheet metal.

FIG. 5 is a cross-section of a detail of a deep-drawn shaped part whichis welded from pieces 37, 38 of sheet metal of different thicknesses andin which the joint 39 is located in a portion shaped by deep drawing.

What is claimed is:
 1. A shaped member of welded pieces of sheet metalof different thickness, more particularly having a metallicanti-corrosion protection, for example of zinc, on at least one side,characterized in that the pieces of sheet metal are joined to oneanother by a laser-beam-butt-welding process and shaped as a unit.
 2. Ashaped member according to claim 1, characterized in that the surfacesof the pieces of sheet metal on one side of the shaped member are lyingin the same plane.
 3. A shaped member according to claim 1,characterized in that a transitional zone from the cut edge to thesurfaces of a projecting piece of sheet metal lies outside the weldingzone.
 4. A shaped member according to claim 1, characterized in that thegreater proportion of the welding zone lies in the thicker piece ofsheet metal.
 5. A shaped member according to claim 1, characterized inthat the joint forms a groove in a transitional zone between the exposedpart of a cut edge of one piece of sheet metal and the offset surface ofthe other piece of sheet metal.